Molecular Mechanisms of Dioxin Action

描述（由申请人提供）：本提案的长期目标是了解二恶英（2,3,7,8-四氯二苯并-对二恶英；TCDD）暴露的生物学反应的分子机制。TCDD是二恶英的原型，也是许多其他有机氯化合物的模型，它产生许多显然不相关的生物效应，从人体内的氯痤疮到发育致畸、肿瘤促进、胸腺萎缩、消耗综合征和实验动物死亡。此外，TCDD，一种啮齿动物致癌物，被强烈怀疑对人类也有致癌性。TCDD生物效应的分子基础在很大程度上是未知的。二恶英是芳香烃（Ah）受体（AHR）的配体，与Ah受体核转运蛋白ARNT作为二聚体，介导细胞色素P450单加氧酶CYP 1家族基因的转录激活。然而，CYP1A1、CYP1A2和cyp1b1基因的激活，虽然是TCDD激活Ah受体最具特征的效应之一，但并不能充分解释TCDD效应的多样性。我们最近对人类肝癌细胞的全球表达谱分析表明，暴露于二恶英诱导或抑制了总共300多个基因，其中抑制更为频繁。诱导可以很容易地用AHR的反激活电位来解释，但基因抑制是活化AHR的一种新效应，在分子水平上尚未表征。本文提出的实验目的是定义和表征激活的AHR与其他转录因子、共调节因子和染色质重塑因子之间的调节相互作用，这些因子负责二恶英对基因表达的影响。这项工作的主要目标是：(1)确定AHR的离散结构域在基因调控中的作用；(2)利用蛋白质组学分析鉴定AHR在基因诱导和抑制中的协同调控伙伴；(3)克隆AHR调控基因启动子，并表征其对二恶英暴露的反应。这些实验的结果将对我们了解接触二恶英和其他有机氯化合物的长期生物学后果至关重要，并将有助于制定充分的理由，以处理因日益增加地接触这些环境物质而引起的健康问题。

DESCRIPTION (provided by applicant): The long-term objective of this proposal is to understand the molecular mechanisms underlying the biological responses to dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin; TCDD) exposure. TCDD, the prototypic dioxin and a model for many other organochlorinated compounds, produces many apparently unrelated biological effects, ranging from chloracne in humans to developmental teratogenesis, tumor promotion, thymic atrophy, wasting syndrome and death in laboratory animals. In addition, TCDD, a rodent carcinogen, is strongly suspected of being carcinogenic also in humans. The molecular basis of the biological effects of TCDD is largely unknown. Dioxin is a ligand for the aromatic hydrocarbon (Ah) receptor (AHR), which, as a dimer with the Ah receptor nuclear translocator protein ARNT, mediates the transcriptional activation of genes in the CYP 1 family of cytochrome P450 monooxygenases. However, activation of the CYP1A1, CYP1A2 and CYP1 B1 genes, although one of the best characterized effects of Ah receptor activation by TCDD, does not adequately explain the diversity of TCDD effects. Our recent global expression profiling analyses of human hepatoma cells shows that exposure to dioxin induces or represses a total of more than 300 genes, with repression being the more frequent. Induction may readily be explained by the transactivating potential of the AHR, but gene repression is a novel effect of the activated AHR that is uncharacterized at the molecular level. The goal of the experiments proposed here is to define and characterize the regulatory interactions between the activated AHR and other transcription factors, co-regulators and chromatin remodeling factors responsible for the effects of dioxin on gene expression. The major objectives of this work are, (1) to define the role of discrete domains of the AHR in gene regulation; (2) to use proteomic analyses to identify AHR coregulatory partners in gene induction and repression; and (3) to clone the promoters of AHR regulated genes and characterize their response to dioxin exposure. Results from these experiments will be crucial for our understanding of the long-range biological consequences of exposure to dioxin and to other organochlorinated compounds and will help formulate an adequate rationale to deal with health problems arising from an ever-increasing exposure to these environmental agents.